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    <a href="../index.html">cppreference.com</a> &gt; <a href=
    "index.html">C/C++ Pre-processor Commands</a> &gt; <a href=
    "sharp.html">#, ##</a>
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    #, ##
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  <p>The # and ## operators are used with the <a href=
  "define.html">#define</a> macro. Using # causes the first argument
  after the # to be returned as a string in quotes. Using ##
  concatenates what&#39;s before the ## with what&#39;s after it.</p>

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    Example code:
  </div>

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    <p>For example, the command</p>
    <pre class="example-code">
   #define to_string( s ) # s           
</pre>

    <p>will make the compiler turn this command</p>
    <pre class="example-code">
   cout &lt;&lt; to_string( Hello World! ) &lt;&lt; endl;               
</pre>

    <p>into</p>
    <pre class="example-code">
   cout &lt;&lt; &quot;Hello World!&quot; &lt;&lt; endl;                
</pre>

    <p>Here is an example of the ## command:</p>
    <pre class="example-code">
   #define concatenate( x, y ) x ## y
   ...
   int xy = 10;
   ...          
</pre>

    <p>This code will make the compiler turn</p>
    <pre class="example-code">
   cout &lt;&lt; concatenate( x, y ) &lt;&lt; endl;             
</pre>

    <p>into</p>
    <pre class="example-code">
   cout &lt;&lt; xy &lt;&lt; endl;              
</pre>

    <p>which will, of course, display &#39;10&#39; to standard
    output.</p>
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    Related topics:
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    <a href="define.html">#define</a>
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